In the period from its publication of its Release 8 specifications (Rel-8) to its development of Release 10 specifications (Rel-10), the 3rd Generation Partnership Project (3GPP) has introduced increasing degrees of support for multi-cell downlink transmissions for High-Speed Downlink Packet Access (HSDPA), alternatively known as multi-carrier HSDPA. Dual-Cell HSDPA (DC-HSDPA) operation, whereby the network could schedule simultaneous transmissions on two adjacent downlink carriers to a mobile terminal (known as User Equipment, or UE, in 3GPP terminology), was standardized in Rel-8. In Rel-9, support for DC-HSDPA in combination with multiple-input multiple-out (MIMO) transmissions was introduced, along with support for Dual-Band DC-HSDPA. The former technique provides a peak data rate of 84 Mbps, while the latter extends the Rel-8 DC-HSDPA feature so that the two configured downlink carriers can be located in different frequency bands.
In Rel-10, 3GPP introduced four-carrier High-Speed Downlink Packet Access (4C-HSDPA) operation, which provides peak downlink data rates of 168 Mbps. Currently, 3GPP is developing support for eight-carrier High-Speed Downlink Packet Access (8C-HSDPA) for standardization in Release 11 of the 3GPP specifications (Rel-11). This technique, whereby as many as eight carriers can be simultaneously used to transmit data to a single UE, will allow peak data rates up to about 336 Mbps.
Many packet data systems, including wireless systems that support HSDPA, support an acknowledged mode transmission of data, in which an ARQ (Automatic Repeat Request) mechanism is used to trigger the retransmission of defective or lost data packets. This acknowledged mode of data transmission is part of the Radio Link Control (RLC) protocol, which is specified for 3GPP systems in “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Link Control (RLC) protocol specification (Release 10),” 3GPP TS 25.322, v 10.1.0 (June 2011). The 3GPP RLC protocol is also more generally described in U.S. Pat. No. 7,870,259, “Method and Transmitter for an Efficient Packet Data Transfer in a Transmission Protocol with Repeat Requests,” the entire contents of which are incorporated herein by reference to provide technical background and context for the inventive techniques, as well as to introduce the devices, methods, and techniques that may be adapted according to the detailed techniques described herein.
Currently, several aspects of the RLC specifications for HSDPA limit the achievable downlink throughput, i.e., the data transfer rates from the base station to mobile terminals or, in 3GPP terms, from the Node B to UEs. More particularly, downlink throughput at the RLC layer is limited by the RLC Sequence Number (SN) space and the maximum configurable size for a RLC Protocol Data Unit (PDU). As a result, the maximum data rates possible with eight-carrier HSDPA (8C-HSDPA) cannot be supported at the RLC layer without RLC timer settings that can otherwise result in a detrimental impact to user and cell capacity. Accordingly, improved RLC techniques are needed.